Redox-Induced Reversible Rearrangement of a Dimetallaallyl Ligand

Organometallics 2007, 26, 1349-1360

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Redox-Induced Reversible Rearrangement of a Dimetallaallyl Ligand on the Trinuclear Cluster of Ruthenium. Mechanistic Aspects of Formation of the Face-Capping µ3-C3 Ring on the Triruthenium Plane Toshiro Takao, Makoto Moriya, and Hiroharu Suzuki* Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan ReceiVed October 11, 2006

The dicationic complexes [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H2Me)(µ-H)]2+ (7a,b; Cp* ) η5-C5Me5), containing a µ3-η3-C3 ring on the Ru3 triangle, were obtained by the reaction of a µ3-methylidyne µ3η1:η3:η1-2-methyldiruthenaallyl complex, (Cp*Ru)3(µ-H)(µ3-η1:η3:η1-CHCMeCH)(µ3-CH) (5a), with 2 equiv of ferrocenium salt. The µ3-η3-C3 ring was structurally characterized for the monocationic complex [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H2Me)]+ (8), which was obtained by deprotonation of a mixture of the regioisomers 7a,b. The carbenic character of the carbons in the µ3-η3-C3 ring was shown in the unusually long C-C bond distances and JC-H values. CV analysis of 5a strongly indicates that transformation of the dimetallaallyl moiety to the µ3-C3 ring occurred on the dicationic Ru3 centers, as well as isolation of a paramagnetic intermediate, [(Cp*Ru)3(µ3-CH)(µ3-η1:η3:η1-CHCMeCH)(µ-H)]+ (6), containing a µ3diruthenaallyl ligand. Introduction Cooperative interaction of the multiple metal centers of the cluster has been shown to direct notable skeletal rearrangement reactions of the hydrocarbyls.1 For example, an unactivated C-C bond of cyclopentadiene was readily cleaved in the triangle reaction field of the triruthenium pentahydrido complex {Cp*Ru(µ-H)}3(µ3-Η)2 (1; Cp* ) η5-C5Me5) at ambient temperature, and a nido-ruthenacyclopentadiene complex, {Cp*Ru(µ-H)}3(µ3-η1:η2:η2:η1-CMedCHCHdCH-) (2), was exclusively obtained (Scheme 1).2 In this reaction, DFT calculations have shown3 that µ3-η2:η2 coordination of the cyclopentadiene is a key step in the C-C bond scission, and these calculations also demonstrate that the C-C bond was effectively activated by the multiple coordination on the cluster. A cluster complex plays the role of a reservoir for holding electrons and, as a result, a multistep redox reaction would be possible between the cluster and the substrate. Reduction and oxidation of the metal sometimes result in the skeletal rearrangement of the hydrocarbyls on the cluster, since the electronic perturbation at the metal centers would be compensated by the change in the coordination mode of the ligand.4 We have reported a hapticity change in the oxidation of a µ3-η2:η2:η2benzene complex:5 two-electron oxidation of {Cp*Ru(µ-H)}3(µ3-η2:η2:η2-C6H6) afforded [{Cp*Ru(µ-H)}3(µ3-η3:η3-C6H6)]2+ (1) Suzuki, H. Eur. J. Chem. 2002, 1009-1023. (2) Suzuki, H.; Takaya, Y.; Takemori, T. J. Am. Chem. Soc. 1994, 116, 10779-10780. (3) Khoroshun, D. V.; Inagaki, A.; Suzuki, H.; Vyboishchikov, S. F.; Musaev, D. G.; Morokuma, K. J. Am. Chem. Soc. 2003, 125, 9910-9911. (4) (a) Edwin, J.; Geiger, W. E.; Salzer, A.; Ruppli, U.; Rheingold, A. L. J. Am. Chem. Soc. 1987, 109, 7893-7894. (b) Geiger, W. E.; Salzer, A.; Edwin, J.; von Philipsborn, W.; Piantini, U.; Rheingold, A. L. J. Am. Chem. Soc. 1990, 112, 7113-7121. (c) Okazaki, M.; Ohtani, T.; Ogino, H. J. Am. Chem. Soc. 2004, 126, 4104-4105. (d) Okazaki, M.; Ohtani, T.; Takano, M.; Ogino, H. Organometallics 2004, 23, 4055-4061. (5) Inagaki, A.; Takaya, Y.; Takemori, T.; Suzuki, H.; Tanaka, M. J. Am. Chem. Soc. 1997, 119, 625-626.

Scheme 1

as a consequence of rotation of the µ3-benzene ligand by 30° on the Ru3 plane (eq 1). Transformation of the alkyne ligand

from perpendicular to parallel coordination upon reduction has been also well documented for the trimetallic complexes.6 (6) (a) Osella, D.; Gobetto, R.; Montangero, P.; Zanello, P.; Cinquantini, A. Organometallics 1986, 5, 1247-1253. (b) Osella, D.; Pospisil, L.; Fieldler, J. Organometallics 1993, 12, 3140-3144.

10.1021/om060932x CCC: $37.00 © 2007 American Chemical Society Publication on Web 02/08/2007

1350 Organometallics, Vol. 26, No. 6, 2007

Takao et al.

Figure 1. Cyclic voltammograms of (a) 5a (0.5 mM) and (b) 3a (1.0 mM) in THF at 25 °C. Conditions: electrolyte, 0.1 M [NBu4](PF6); working electrode, Pt; scan rate, 50 mV/s. Potentials are referenced to Fc/Fc+.

We have recently reported a novel type of skeletal rearrangement of the C3 moiety of a µ3-η1:η3:η1-diruthenaallyl complex, (Cp*Ru)3(µ-H)4(µ3-η1:η3:η1-CHCRCMe) (3a, R ) H; 3b, R ) Me),7 promoted by chemical oxidation.8 Treatment of 3 with 2 equiv of the hexafluorophosphate salt of the ferrocenium cation, [Cp2Fe]+ (Fc+; Cp ) η5-C5H5), resulted in the exclusive formation of a hexafluorophosphate salt of the monocationic complex [{Cp*Ru(µ-H)}3(µ3-η3-C3HRMe)]+ (4), which pos-

sessed a µ3-η3-C3 ring on the Ru3 plane (eq 2). This result is quite different from the thermal reaction of 3 (eq 3).9 The µ3-

diruthenaallyl complex 3 equilibrated with a µ3-vinylidene complex at 50 °C, and it underwent C-C bond cleavage to yield a µ3-methylidyne-µ3-η2(||)-alkyne complex at 80 °C. The formation of the µ3-η3-C3 ring likely proceeds via a sequence of reactions, namely, two steps of one-electron oxidation, deprotonation, and C-C bond formation. In order to elucidate the mechanistic detail of the µ3-C3 ring formation, we investigated oxidation of the µ3-methylidyne µ3-η1:η3:η1diruthenaallyl complex (Cp*Ru)3(µ-H)(µ3-η1:η3:η1-CHCMeCH)(µ3-CH) (5a), which was obtained by the thermolysis of the nido-ruthenacyclopentadiene complex 2 (eq 4).10 Since 5a

contains a µ3-methylidyne ligand, the redox potentials of 5a were considerably different from those of 3 and enabled us to isolate several important intermediates of this skeletal rearrangement. We report herein the oxidation of the µ3-η1:η3:η1diruthenaallyl complex 5a and reactivity of a dicationic complex having a µ3-C3 ring.

Results and Discussion One-Electron Oxidation of the µ3-Methylidyne µ3-η1:η3: Complex 5a. In order to assess the influence of the µ3-methylidyne ligand, a solution of 5a was subjected to a CV scan. The cyclic voltammogram of 5a is depicted in Figure 1a, which showed reversible and irreversible one-electron waves. The reversible wave at E1/2 ) -718 mV indicates the formation of a chemically stable 47-electron species. The second anodic peak was observed at Ep,a ) +5.70 mV, but the corresponding cathodic peak was diminished, which implies that the second process is irreversible. There have been only two reports so far on the electrochemical behavior of a triruthenium carbonyl cluster having a µ3η1-2-Methyldiruthenaallyl

(7) Takemori, T.; Suzuki, H.; Tanaka, M. Organometallics 1996, 15, 4346-4348. (8) Takao, T.; Inagaki, A.; Murotani, E.; Imamura, T.; Suzuki, H. Organometallics 2003, 22, 1361-1363. (9) Takemori, T.; Inagaki, A.; Suzuki, H. J. Am. Chem. Soc. 2001, 123, 1762-1763.

(10) Inagaki, A.; Takao, T.; Moriya, M.; Suzuki, H. Organometallics 2003, 22, 2196-2198.

Rearrangement of a Dimetallaallyl Ligand

diruthenaallyl ligand.11 Keister and co-workers found two steps of one-electron-oxidation processes for the series of triruthenium complexes Ru3(CO)9-n(PPh3)n(µ3-η1:η3:η1-XCCRCR′)(µ-H) (n ) 0-3; X ) OMe, NMe2; R ) Me, H; R′ ) Me, OEt), and they noted that the first oxidation process was reversible to quasi-reversible and the second oxidation was irreversible.11b These redox peaks of the carbonyl clusters appeared at a considerably positive region in comparison with those found for 5a and 3a. For example, the E1/2 and Ep,a values of the triruthenium complex Ru3(CO)7(PPh3)2(µ3-MeOCCMeCMe)(µH) were reported to be 0.27 and 0.74 V, respectively (referenced to Fc/Fc+).11b In this study, it has been also noted that both π-donor substituents on the diruthenaallyl moiety and σ-donor substituents on the metal center lower the oxidation potentials. Therefore, lowering of the oxidation potentials of 5a and 3a was most likely due to both electron-rich metal centers stemming from the three Cp* ligands and the lack of electron-withdrawing carbonyl ligands. While two redox waves were found in the cyclic voltammogram of 5a, as found in that of the diruthenaallyl tetrahydrido complex 3a (Figure 1b), both peaks considerably shift toward the positive direction; E1/2 of the first reversible wave shifted by +0.27 V, and Ep,a of the second irreversible wave also underwent a positive shift by +0.15 V. This shows that oxidation of the metal centers becomes difficult when the µ3methylidyne ligand is introduced. The µ3-methylidyne ligand probably contributes to stabilizing the HOMO of 5a. The reaction of 3a with an equimolar amount of Fc+ yielded 4a as a major product instead of the intermediary 47e species anticipated from the CV analysis shown in Figure 1b. In contrast, treatment of 5a with an equimolar amount of Fc+ resulted in the exclusive formation of a hexafluorophosphate salt of the paramagnetic complex [(Cp*Ru)3(µ3-CH)(µ3-CHCMeCH)(µH)]+ (6) (eq 5). This is probably due to the shift of the oxidation

potentials toward the positive direction, which caused a considerable decrease of the rate of the second oxidation. Keister and co-workers detected the one-electron-oxidation products of the triruthenium carbonyl clusters Ru3(CO)9-n(PPh3)n(µ3-η1:η3: η1-Me2NCCHCMe)(µ-H) and Ru3(CO)9-n(PPh3)n{µ3-η1:η3:η1MeOCCHC(OEt)}(µ-H) (n ) 2, 3), by means of the EPR spectroscopy below -40 °C.11b On the basis of the reversibility of the redox wave of the carbonyl clusters, the paramagnetic species adopted a structure similar to that of the neutral species, but the researchers did not mention the structure of the paramagnetic species, due to the instability of the compounds. (11) (a) Zanello, P.; Aime, S.; Osella, D. Organometallics 1984, 3, 13741378. (b) Yao, H.; McCargar, R. D.; Allendoerfer, R. D.; Keister, J. B. Organometallics 1993, 12, 4283-4285.

Organometallics, Vol. 26, No. 6, 2007 1351

The 1H NMR spectra of a tetraphenylborate salt of 6, which was obtained by the reaction of 6 with excess NaBPh4, showed a broad signal at δ 43.68 (w1/2 ) 2120 Hz). This implied the formation of a paramagnetic 47e species. Since a single crystal suitable for the diffraction studies has not been obtained, structure determination of 6 has not been performed yet. However, quantitative reproduction of 5a by one-electron reduction using Cp*2Co strongly supported that the skeletal rearrangement did not occur at this step, which is quite consistent with the reversibility of the first redox wave in the cyclic voltammogram. Therefore, it is concluded that complex 6 is a monocationic µ3-methylidyne µ3-η1:η3:η1-2-methyldiruthenaallyl complex, as shown in eq 5. Two-Electron Oxidation of the µ3-Methylidyne µ3-η1:η3: 1 η -2-Methyldiruthenaallyl Complex 5a. Treatment of 5a with 2 equiv of Fc+ or further oxidation of the monocationic complex 6 by using an equimolar amount of Fc+ in THF afforded a mixture of hexafluorophosphate salts of the dicationic complexes [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H2Me)(µ-H)]2+ (7a,b) as a red precipitate (eq 6). These dicationic complexes were soluble in

acetone and CH2Cl2, while they were sparingly soluble in THF and MeOH. Since complexes 7a,b were in equilibrium in solution, only the averaged 1H NMR spectrum was obtained at room temperature. Therefore, we characterized them on the basis of the 1H and 13C NMR spectra recorded at -70 °C. The molecular ratio between 7a and 7b was estimated as 67:33 at -70 °C. The signals of the ring carbons of the major isomer 7a were observed at δ 171.8 (d, JC-H ) 196.9 Hz, -CH) and 132.1 (s, -CMe) in the 13C NMR spectra. The JC-H value of 196.9 Hz is comparable to those of the structurally well-defined complexes containing a µ3-η3-C3 ring; the JC-H values of the µ3-η3-C3 ring were 184.7 and 177 Hz for [{Cp*Ru(µ-H)}3(µ3-η3-C3H2Me)]+ (4a)8 and (Cp*Ru)3(µ3-η3-C3H2Me)(µ3-CO),12 respectively. These values are considerably larger than the JC-H values of the µ3-dimetallaallyl ligand (JC-H ) 135.3-154.0 and 146.4158.3 Hz for the terminal (C1 and C3) and the central (C2) carbons, respectively).7,10,13 Formation of the face-capping µ3η3-C3 ring was confirmed by the X-ray diffraction study for a tetraphenylborate salt of [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H2Me)]+ (8), which was obtained by deprotonation of the dicationic mixture (vide infra). (12) Trakarnpruk, W.; Arif, A. M.; Ernst, R. D. Organometallics 1994, 13, 2423-2429. (13) (a) Beanan, L. R.; Keister, J. B. Organometallics 1985, 4, 17131721. (b) Nuel, D.; Mathieu, R. Organometallics 1988, 7, 16-21. (c) Takao, T.; Takemori, T.; Moriya, M.; Suzuki, H. Organometallics 2002, 21, 51905203.


Takao et al.

Figure 2. Variable-temperature 1H NMR spectra of the dicationic complexes [(Cp*Ru)3(µ3-CH)(µ3-η3-CHCMeCH)(µ-H)]2+ (7a,b) showing the regions for the methine protons (a) and the hydrides (b) in acetone-d6. Signals marked with an asterisk (*) are derived from residual toluene in the sample. The signal found at δ 8.55 marked with a pound sign (#) is derived from a decomposed product due to moisture, and the methine signal of the µ3-C3 ring of 8 formed by deprotonation is also found at δ 7.86.

The two methine proton resonances of the µ3-η3-C3 ring of 7a were observed to be equivalent at δ 9.18 (2H) as a singlet. This suggests that complex 7a has a plane of symmetry bisecting the µ3-η3-C3 ring. Therefore, the hydrido ligand must be located on the Ru-Ru edge bridged by the µ-CMe group. Because the proportion of 7b in solution in the isomeric mixture was low at -70 °C, the 13C signals derived from 7b were not fully assigned, and the JC-H data of the ring carbon characteristic of the µ3-η3-C3 ring structure were missing. Complex 7b was thus characterized mainly on the basis of the 1H NMR spectra. Although spectroscopic evidence for the µ 3 η3-C3 ring of 7b was not obtained, the fact that deprotonation of the mixture of 7a and 7b afforded only one isomer, 8, containing a µ3-η3-C3 ring (vide infra), strongly suggests that complex 7b also contains a µ3-η3-C3 ring, just as 7a does. And, the 1H NMR data indicated that 7b was regioisomeric with 7a with respect to the position of the hydrido ligand. The hydride of 7b was most likely coordinated to the Ru-Ru edge bridged by the µ-CH group. The two methine protons of the C3 ring are, therefore, placed in nonequivalent environments. In the 1H NMR spectra, one of them was observed at δ 9.27 as a doublet (JH-H ) 2.4 Hz) and the other was observed at δ 6.89 as a pseudotriplet due to additional coupling with the hydrido ligand (JH-H ) 2.4 and 2.4 Hz). In order to confirm the equilibrium between 7a and 7b, we prepared an unsubstituted µ3-η3-C3 complex, [(Cp*Ru)3(µ3-η3C3H3)(µ3-CH)(µ-H)]2+ (7c), through the two-electron oxidation

of the unsubstituted diruthenaallyl complex (Cp*Ru) 3(µ3-η1:η3: η1-CHCHCH)(µ3-CH)(µ-H) (5b)14 (eq 7). Treatment of 5b with 2 molar equiv of Fc+ brought about a rapid color change and resulted in the quantitative formation of a red precipitate of 7c. Exclusive formation of 7c was confirmed by means of 1H and 13C NMR spectroscopy. Signals for the hydride of 7a and 7b were observed at δ -15.37 and -15.00 in the 1H NMR spectra measured at -70 °C, respectively (Figure 2b). As mentioned above, the intensity ratio of the signals was 67:33 at -70 °C. They broadened with an increase in the temperature. They coalesced into a broad signal at 10 °C. Signals for both the µ3-methylidyne proton and the methyl proton on the µ3-η3-C3 ring of 7a,b also coalesced at ambient temperature. Because of the efficiently rapid interconversion between 7a and 7b stemming from the dynamic behavior of the hydrido ligand, two signals of the Cp* groups were observed at δ 2.06 and 2.08 in an intensity ratio of 2:1. These two signals of the Cp* groups never broadened and coalesced, in spite of the rise in temperature. This clearly shows that the µ3-η3-C3 ring is rigid and rotation of the µ3-η3-C3 ring was negligible, at least within the NMR time scale. The µ3-η3-C3 ring of the monocationic complex [{Cp*Ru(µ-H)}3(µ3-η3-C3HRMe)]+ (4) has been also revealed to be rigid.8 Deprotonation of the Dicationic Mixture 7a,b. The dicationic mixture 7a,b undergoes deprotonation on dissolution in acetone containing adventitious water. Deprotonation was accelerated by the addition of MeOH to the acetone solution of 7 due to an increase in polarity of the solvent (see the Supporting Information). Deprotonation of the dicationic mixture quantitatively proceeded by the addition of a base, such as amine. Treatment of 7a,b with an excess amount of triethylamine in (14) Complex 5b was obtained by the thermolysis of the µ3-η2-vinylidene µ3-η2(||)-ethyne complex (Cp*Ru)3(µ3-η2(||)-HCCH)(µ3-η2-CdCH2)(µH).13c Details of the formation of 5b, including C-C bond cleavage and formation across the Ru3 plane, will be published elsewhere.


Organometallics, Vol. 26, No. 6, 2007 1353 Table 1. Selected Bond Distances (Å) and Angles (deg) for 8 Ru(1)-Ru(2) Ru(1)-C(3) Ru(2)-C(1) Ru(3)-C(1) C(2)-C(3) C(3)-C(4) Ru(1)-Ru(3) Ru(1)-C(4)

Figure 3. Molecular structure and labeling scheme of 8 with thermal ellipsoids at the 40% probability level. The anionic moiety (BPh4-) is omitted for clarity.

CH2Cl2 resulted in quantitative formation of a hexafluorophosphate salt of the monocationic complex [(Cp*Ru)3(µ3-CH)(µ3η3-C3H2Me)]+ (8), containing a µ3-η3-C3 ring (eq 8). Complex

8 was fully characterized on the basis of the 1H and 13C NMR and IR spectra as well as analytical data. Protonation of 8 by CF3SO3H afforded the dicationic mixture 7a,b. A signal assignable to the hydride of the dicationic mixture appeared at δ -15.48. However, no reaction occurred with CF3COOH. In the 1H NMR spectra of 8, a signal of the methine proton of the µ3-η3-C3 ring was observed at δ 7.77. The resonances for the ring carbons were observed at δ 109.9 (s, -CMe) and 158.2 (d, JC-H ) 189.1 Hz, -CH). These shifts are slightly higher than those for the dicationic complexes 7a,c. The JC-H value of 189.1 Hz was smaller than that observed in 7a by 8 Hz. This is probably due to reduction of the s character of the hybrid orbital at the ring carbon in 8 in comparison with that of 7a as a result of enhanced back-donation from the metal center to the C3 ring. A single crystal suitable for the X-ray diffraction studies was obtained by changing the counteranion from PF6- to BPh4-. The structure of 8 is shown in Figure 3, and relevant bond lengths and angles are given in Table 1. The crystal data for 8-BPh4 are given in the Experimental Section (Table 4). The C3 plane is approximately parallel to the Ru3 triangle in staggered form, which is very similar to the case for the reported tris(µ-carbene) complexes [{Cp*Ru(µ-H)}3(µ3-η3-C3HMe2)]+ (4b)8 and (Cp*Ru)3(µ3-CO)(µ3-η3-C3H2Me).12 The average RuRu distance (2.70 Å) corresponds to an Ru-Ru single bond and is slightly shorter than those of 4b (average 2.81 Å). The difference in the Ru-Ru bond lengths between 8 and 4b likely arises from the µ3-methylidyne ligand placed on the opposite face of the Ru3 plane. The µ3-methylidyne ligand seems to bind the ruthenium atoms more tightly than does the µ-hydrido ligand.

Ru(2)-Ru(1)-Ru(3) C(3)-Ru(1)-C(4) Ru(3)-Ru(2)-C(2) Ru(1)-Ru(3)-C(4) Ru(1)-C(1)-Ru(2) Ru(2)-C(2)-Ru(3) C(3)-C(2)-C(4) Ru(1)-C(3)-Ru(2) C(2)-C(3)-C(4) Ru(3)-C(4)-C(2) Ru(2)-Ru(1)-C(3) Ru(1)-Ru(2)-Ru(3) C(2)-Ru(2)-C(3) Ru(2)-Ru(3)-C(2) Ru(1)-C(1)-Ru(3)

2.7018(4) 2.067(2) 2.005(2) 2.010(2) 1.605(3) 1.582(3) 2.6870(4) 2.055(2) 60.126(11) 45.12(9) 49.46(6) 49.20(6) 84.48(8) 81.11(8) 58.93(14) 81.85(8) 60.71(14) 67.93(12) 48.92(6) 59.665(10) 45.69(9) 49.43(6) 83.78(8)

Ru(2)-C(2) Ru(3)-C(2) C(2)-C(5) Ru(1)-C(1) Ru(2)-Ru(3) Ru(2)-C(3) Ru(3)-C(4) C(2)-C(4) Ru(2)-C(2)-C(3) C(3)-C(2)-C(5) Ru(1)-C(3)-C(4) Ru(1)-C(4)-Ru(3) C(2)-C(4)-C(3) Ru(3)-Ru(1)-C(4) Ru(1)-Ru(2)-C(3) Ru(1)-Ru(3)-Ru(2) C(2)-Ru(3)-C(4) Ru(2)-C(1)-Ru(3) Ru(2)-C(2)-C(5) C(4)-C(2)-C(5) Ru(2)-C(3)-C(2) Ru(1)-C(4)-C(3)

2.075(2) 2.077(2) 1.496(3) 2.014(2) 2.6996(5) 2.057(2) 2.049(2) 1.610(3) 66.56(11) 120.8(2) 67.04(12) 81.79(8) 60.35(14) 49.00(6) 49.23(6) 60.209(11) 45.95(9) 84.52(8) 131.06(17) 121.45(19) 67.75(11) 67.84(12)

The Ru-Ru length is rather close to that of the neutral complex (Cp*Ru)3(µ3-CO)(µ3-η3-C3H2Me) (average 2.74 Å),12 which contains a µ3-carbonyl ligand. The C3 ring forms a nearly equilateral triangle with edges of 1.605(3), 1.610(3), and 1.582(3) Å. Notably, these C-C bond lengths of the C3 ring are significantly longer than that for the normal C-C single bond (C(sp3)-C(sp3) ) 1.537 ( 0.005 Å).15 In contrast, the C-C bond lengths of mononuclear η3-C3R3 complexes mostly lie in the range from 1.40 to 1.45 Å.16 Such an elongation of the C-C bond is the most striking feature of the trinuclear µ3-η3-C3 complex. The average C-C bond lengths of other trinuclear µ3-η3-C3 complexes are also significantly large (4b, 1.56 Å;8 (Cp*Ru)3(µ3-CO)(µ3-η3-C3H2Me), 1.58 Å12). In addition, the bend-back angles of the substituents from the C3 plane are significantly larger than those for the mononuclear η3-cyclopropenyl complexes; C(5), H(2), and H(3) are bent away by 53.6, 55.7, and 55.4° from the C3 plane, respectively. Those of the mononuclear η3-cyclopropenyl complexes lie in the range from 13.7 to 43.5°.16 Long C-C bond lengths and large bend-back angles indicate that the C3 ring is coordinated to the Ru3 core in a manner different from those found in the mononuclear η3-cyclopropenyl complexes. These structural features found in 8 strongly suggest the carbenic character of the ring carbon and are quite consistent with the large JC-H values, 177-209 Hz (vide supra). (15) Spec. Publ. Chem. Soc. 1965, No. 18, S14s-S15s. (16) For example: (a) Weaver, D. L.; Tuggle, R. M. J. Am. Chem. Soc. 1969, 91, 6506-6507. (b) Tuggle, R. M.; Weaver, D. L. Inorg. Chem. 1971, 10, 1504-1510. (c) McClure, M. D.; Weaver, D. L. J. Organomet. Chem. 1973, 54, C59-C61. (d) Chiang, T.; Kerber, R. C.; Kimball, S. D.; Lauher, J. W. Inorg. Chem. 1979, 18, 1687-1691. (e) Gompper, R.; Bartmann, E.; No¨th, H. Chem. Ber. 1979, 112, 218-233. (f) Drew, M. G. B.; Brisdon, B. J.; Day, A. J. Chem. Soc., Dalton Trans. 1981, 1310-1316. (g) Schrock, R. R.; Pedersen, S. F.; Churchill, M. R.; Ziller, J. W. Organometallics 1984, 3, 1574-1583. (h) Hughes, R. P.; Reisch, J. W.; Rheingold, A. L. Organometallics 1985, 4, 1754-1761. (i) Churchill, M. R.; Fettinger, J. C. J. Organomet. Chem. 1985, 290, 375-386. (j) Hughes, R. P.; Lambert, J. M.; Whitman, D. W.; Hubbard, J. L.; Henry, W. P.; Rheingold, A. L. Organometallics 1986, 5, 789-797. (k) Cecconi, F.; Ghilardi, C. A.; Midollini, S.; Moneti, S.; Orlandini, A. Angew. Chem., Int. Ed. Engl. 1986, 25, 833-834. (l) Schrock, R. R.; Murdzek, J. S.; Freudenberger, J. H.; Churchill, M. R.; Ziller, J. W. Organometallics 1986, 5, 25-33. (m) Hughes, R. P.; Tucker, D. S.; Rheingold, A. L. Organometallics 1993, 12, 30693074. (n) Blunden, R. B.; Cloke, F. G. N.; Hitchcock, P. B.; Scott, P. Organometallics 1994, 13, 2917-2919. (o) Ghilardi, C. A.; Innocenti, P.; Midollini, S.; Orlandini, A.; Vacca, A. J. Chem. Soc., Dalton Trans. 1995, 1109-1113.


Takao et al. Scheme 2

Oxidation of 5a generating the monocationic µ3-η3-C3 complex 8 proceeds by way of two initial steps of one-electron oxidation, leading to the dicationic µ3-diruthenaallyl complexes 9 via the monocationic complex 6, skeletal rearrangement involving C-C bond formation on the dicationic metal centers of 9, and subsequent deprotonation from the dicationic hydrido complex 7, as shown in Scheme 2. Unfortunately, signals assignable to 9 were not detected when the reaction was monitored by means of 1H NMR spectroscopy. This is likely due to rapid conversion of 9 to 7a,b via a skeletal rearrangement of the diruthenaallyl moiety. A C3-ring ligand was formed via bond formation between the terminal carbon atoms of the allylic moiety of the dicationic intermediate 9. Direct bond formation across the two metal centers has been well investigated in A-frame-type complexes.17 There is still argument regarding the mechanism, but some of the reactions were considered to proceed via a 1,2-shift of the alkyl group followed by the usual reductive elimination at a metal center. At present, we do not have any positive evidence to show how the C3 ring in 7 was formed. Reduction of the Dicationic Mixture 7a,b. Treatment of the dicationic mixture 7a,b, with 2 equiv of sodium naphthalenide at 25 °C resulted in formation of a mixture of two stereoisomeric neutral diruthenaallyl complexes, 5a,c, in the ratio 65:35 (eq 9). The diruthenaallyl complexes 5a,c were formed

as the result of C(H)-C(H) and C(Me)-C(H) bond cleavage of the µ3-η3-C3 ring, respectively. Further reduction leading to the formation of an anionic complex was not observed during this reaction. This reduction is quite different from the reduction

of carbonyl dimetallaallyl clusters, which yields an anionic species followed by degradation.11a Since 5a,c could not be separated from each other by column chromatography, they were characterized as a mixture by means of 1H and 13C NMR spectroscopy. Complex 5a was unambiguously identified by comparing the spectra with those of the authentic sample.10 In the 1H NMR spectra of the mixture, three Cp* signals arising from 5c were observed at δ 1.52, δ 1.83, and δ 1.88, while those of 5a were observed as a set of two signals with an intensity ratio of 2:1 (δ 1.58 and 1.90). The resonance of the methine protons of 5a was observed at δ 8.24 as a singlet, and those of 5c appeared at δ 5.43 (dd, JH-H ) 5.6, 4.0 Hz) and δ 8.48 (d, JH-H ) 5.6 Hz) with mutual coupling. Long-range coupling between the hydride and the allylic proton located at the 2-position has been often observed for the µ3-dimetallaallyl complexes, and the value of 4.0 Hz for 5c lies in the reported range (0.5-5.0 Hz).13,15,18 The 1H NMR spectrum of 5c was quite similar to that of the µ3-ethylidyne µ3-η1:η3:η1-1-methyldiruthenaallyl complex 5d (Chart 1), which was synthesized by the reaction of {Cp*Ru(µ-H)}3(µ3-H)2 (1) with three molecules of acetylene.13c The 13C NMR spectrum was also consistent with this structure. Complexes 5a,c were thermally stable and did not decompose, even at 160 °C. In addition, the ratio between 5a and 5c did not change upon heating at 160 °C for 24 h. This shows that isomerization between 5a and 5c did not take place, at least at 160 °C. Thus, the ratio of 5a to 5c seems to be kinetically (17) For example: (a) Stockland, R. A., Jr.; Janka, M.; Hoel, G. R.; Rath, N. P.; Anderson, G. K. Organometallics 2001, 20, 5212-5219. (b) Kramarz, K. W.; Eisenberg, R. Organometallics 1992, 11, 1997-1999. (c) Azam, K.; Puddephatt, R. J. Organometallics 1983, 2, 1396-1399. (18) (a) Bruce, M. I.; Cairns, M. A.; Cox, A.; Green, M.; Smith, M. D. H.; Woodward, P. J. Chem. Soc., Chem. Commun. 1970, 735. (b) Cox, A.; Woodward, P. J. Chem. Soc. A 1971, 3559-3603. (c) Evans, M.; Hursthouse, M.; Randall, E. W.; Rosenberg, E. J. Chem. Soc., Chem. Commun. 1972, 545-546. (d) Gambino, O.; Valle, M.; Aime, S.; Vaglio, G. A. Inorg. Chim. Acta. 1974, 8, 71-75. (e) Castiglioni, M.; Milone, L.; Osella, D.; Vaglio, G. A.; Valle, M. Inorg. Chem. 1976, 2, 394-396. (f) Jangala, C.; Rosenberg, E.; Skinner, D.; Aime, S.; Milone, L.; Sappa, E. Inorg. Chem. 1980, 19, 1571-1575. (g) Aime, S.; Gobetto, R.; Osella, D.; Milone, L.; Rosenberg, E. Organometallics 1982, 1, 640-644. (h) Churchill, M. R.; Lake, C. H.; Lashewycz-Rubycz, R. A.; Yao, H.; McCargar, R. D.; Keister, J. B. J. Organomet. Chem. 1993, 452, 151-160. (i) Yao, H.; McCargar, R. D.; Allendoerfer, R. D.; Keister, J. B. Organometallics 1993, 12, 4283-4285. (j) Kallinen, K. O.; Ahlgre´n, M.; Pakkanen, T. T.; Pakkanen, T. A. J. Organomet. Chem. 1996, 510, 37-43. (k) Bruce, M. I.; Fun, H.-K.; Nicholson, B. K.; Shawkataly, O.; Thomson, R. A. J. Chem. Soc., Dalton Trans. 1998, 751-754. (l) Ellis, D.; Farrugia, L. J. J. Cluster Sci. 2001, 12, 243-257. (m) Xia, C.-G.; Bott, S. G.; Richmond, M. G. J. Chem. Crystallogr. 2003, 33, 681-687.


Organometallics, Vol. 26, No. 6, 2007 1355

Chart 1

Scheme 3

controlled in the reduction step, and the ratio represents the strength of the C-C bond of the µ3-C3 ring; i.e., the C(H)C(H) bond was more readily cleaved than the C(Me)-C(H) bond by ca. 4 times. Chisholm et al. reported that two CMe groups in the µ-allyl group of (Me3SiCH2)4W2(µ-CSiMe3)(µ-CMeCMeCSiMe3) mutually exchange positions within the NMR time scale by way of a µ-C3 ring intermediate (Scheme 3).19a Similar skeletal rearrangement involving formation of a µ3-C3 ring intermediate was also proposed for the formation of a trimetallic dimetallaallyl complex by Stone and co-workers.19b Thus, the formation of 5c by the reduction of 7a,b, which was formed by the oxidation of 5a, could be a good model for the some unusual skeletal rearrangements performed on a multimetallic center. Formation of a Dicationic µ3-η1:η3:η1-2-Methyldiruthenaallyl Complex. As mentioned above, we proposed the dicationic µ3-diruthenaallyl complex 9 as an intermediate of the twoelectron oxidation of 5a. Although no direct evidence of the formation of 9 was obtained, we fortunately isolated a hexafluorophosphate salt of dicationic complex 10 in the reaction of 7 with chloroform. The dicationic complex 10 has a µ3-diruthenaallyl moiety analogous to that of the dicationic intermediate 9. Treatment of the mixture 7a,b with the chlorinated solvents CH2Cl2, CHCl3, and CCl4 resulted in substitution of the hydrido ligand with chloride and afforded the dicationic µ3-methylidyne µ-chloro µ3-η1:η3:η1-2-methyldiruthenaallyl complex [(Cp*Ru)3(µ3-CH)(µ3-η1:η3:η1-CHCMeCH)(µ-Cl)]2+ (10) (eq 10). While the reaction of the dicationic mixture 7 with CH2Cl2 required heating in a sealed bottle at 100 °C, the reaction with CHCl3 proceeded smoothly at room temperature. Although the reaction of 7 with CCl4 took place rapidly, several unidentified products (19) (a) Chisholm, M. H.; Heppert, J. A.; Huffman, J. C. J. Am. Chem. Soc. 1984, 106, 1151-1153. (b) Jeffery, J. C.; Mead, K. A.; Razay, H.; Stone, F. G. A.; Went, M. J.; Woodward, P. J. Chem. Soc., Chem. Commun. 1981, 867-868.

were obtained in addition to 10. During these reactions, a considerable amount of the monocationic complex 8 was formed as a result of deprotonation. Complex 10 was isolated by recrystallization from the cold CH2Cl2 solution of the mixture and fully characterized by means of 1H and 13C NMR and IR spectra as well as elemental analysis. A characteristic feature of the NMR data of 10 is the significant downfield shift of the signals of the allylic moiety. In the 1H NMR spectra, the methine signal of the µ3diruthenaallyl ligand of 10 was observed at δ 10.09 as a singlet. This value is lower by about 2 ppm than that of the neutral diruthenaallyl complex 5a (δ 8.24). The 13C signals of the methine carbons of the µ3-diruthenaallyl moiety of 10 and 5a are δ 195.4 (d, JC-H ) 166.7 Hz) and 174.6 (d, JC-H ) 141.9 Hz), respectively. The increase in the JC-H value implies weakening of the back-donation from the metal center to the allylic moiety in 10, owing to the reduction in electron density in 10. X-ray diffraction studies were performed by the use of a dark green single crystal obtained from cold CH2Cl2 solution at -30 °C. The structure of 10 is represented in Figure 4, and selected bond lengths and angles are given in Table 2. To the best of our knowledge, this is the first structurally elucidated example of a cationic µ3-diruthenaallyl complex. Figure 4 clearly shows the µ3-diruthenaallyl structure of 10. Although the NMR studies indicate weak back-donation from the cationic metal centers to the allylic moiety, the C-C bond lengths (C(2)-C(3), 1.425(3) Å; C(3)-C(4), 1.430(3) Å) are not so different from that of the neutral 5a (1.41 Å). These values lie in the range reported for the µ3-diruthenaallyl complexes.7,10,13c,19a-d,h,j-l,20 Reaction of the Dicationic Mixture with Carbon Monoxide. The presence of the µ3-diruthenaallyl isomer 9 in the equilibrium was also implied by the reaction of the mixture of dicationic complexes 7a,b with carbon monoxide. Treatment of the mixture with 1 atm of CO in CH2Cl2 solution at room temperature resulted in quantitative formation of the hexafluorophosphate salt of the monocationic µ3-methylidyne µ-carbonyl µ3-η1:η3:η1-2-methyldiruthenaallyl complex [(Cp*Ru)3(µ3-CH)(µ3-η1:η3:η1-CHCMeCH)(µ-CO)]+ (11) (eq 11). The µ3-diru-

thenaallyl complex 11 was characterized by means of 1H and NMR and IR spectroscopy. A red single crystal of the tetraphenylborate salt of 11 suitable for the diffraction studies was obtained by changing the counteranion to BPh4-, and the diruthenaallyl structure can be confirmed by the X-ray diffraction studies. There were two independent molecules in the unit 13C


Takao et al.

Figure 4. Molecular structure and labeling scheme of 10 with thermal ellipsoids at the 40% probability level. The anionic moiety (PF6-) and solvent molecules (CH2Cl2) are omitted for clarity. Table 2. Selected Bond Distances (Å) and Angles (deg) for 10 Ru(1)-Ru(2) Ru(1)-C(4) Ru(2)-C(1) Ru(3)-C(1) Ru(3)-C(4) C(3)-C(5) Ru(1)-Ru(3) Ru(1)-Cl(1)

2.6775(3) 2.031(2) 2.020(2) 2.006(5) 2.131(2) 1.508(3) 2.7357(3) 2.3446(6)

Ru(2)-Ru(1)-Ru(3) 60.663(7) Ru(2)-Ru(1)-C(4) 86.41(7) Ru(3)-Ru(1)-C(4) 50.50(7) C(1)-Ru(1)-C(4) 97.07(10) Ru(1)-Ru(2)-C(1) 48.32(7) Ru(3)-Ru(2)-C(1) 47.02(7) Cl(1)-Ru(2)-C(2) 83.19(7) Ru(1)-Ru(3)-C(1) 47.24(7) Ru(2)-Ru(3)-C(1) 47.43(7) C(1)-Ru(3)-C(2) 94.39(9) Ru(2)-C(2)-Ru(3) 82.31(9) C(2)-C(3)-C(4) 116.4(2) Ru(1)-C(4)-Ru(3) 82.16(8) Ru(2)-Ru(1)-Cl(1) 55.212(16) Ru(3)-Ru(1)-Cl(1) 100.283(17) Cl(1)-Ru(1)-C(1) 103.47(7) Ru(1)-Ru(2)-Ru(3) 60.721(7) Ru(1)-Ru(2)-C(2) 86.50(7) Ru(3)-Ru(2)-C(2) 50.31(7) C(1)-Ru(2)-C(2) 96.90(9)

Ru(2)-C(2) Ru(3)-C(2) C(2)-C(3) Ru(1)-C(1) Ru(2)-Ru3) Ru(2)-Cl(1) Ru(3)-C(3) C(3)-C(4) Ru(1)-Ru(3)-C(2) Ru(2)-Ru(3)-C(2) C(1)-Ru(3)-C(4) Ru(2)-C(2)-C(3) C(2)-C(3)-C(5) Ru(1)-C(4)-C(3) Ru(2)-Ru(1)-C(1) Ru(3)-Ru(1)-C(1) Cl(1)-Ru(1)-C(4) Ru(1)-Ru(2)-Cl(1) Ru(3)-Ru(2)-Cl(1) Cl(1)-Ru(2)-C(1) Ru(1)-Ru(3)-Ru(2) Ru(1)-Ru(3)-C(4) Ru(2)-Ru(3)-C(4) C(2)-Ru(3)-C(4) Ru(3)-C(2)-C(3) C(4)-C(3)-C(5) Ru(3)-C(4)-C(3)

2.030(2) 2.123(2) 1.425(3) 2.014(2) 2.7341(3) 2.3458(6) 2.244(2) 1.430(3) 83.25(7) 47.37(6) 94.18(9) 122.99(18) 121.2(2) 122.99(17) 48.50(7) 47.00(7) 82.93(7) 55.171(15) 100.297(16) 103.25(7) 58.616(7) 47.34(7) 83.09(6) 69.56(9) 75.61(14) 121.8(2) 75.26(14)

cell, and one of them contains a disordered structure in the diruthenaallyl moiety and the µ-carbonyl group. Figure 5 represents the structure of the nondisordered molecule of 11, and relevant bond lengths and angles are given in Table 3. Figure 5 clearly shows the µ3-diruthenaallyl structure of 11. The C-C bond lengths of the allylic moiety are almost the same (20) (a) Parkins, A. W.; Fischer, E. O.; Huttner, G.; Regler, D. Angew. Chem., Int. Ed. Engl. 1970, 9, 633. (b) Aime, S.; Osella, D.; Deeming, A. J.; Arce, A. J.; Hursthouse, M. B.; Dawes, H. M. J. Chem. Soc., Dalton Trans. 1986, 1459-1463. (c) Ziller, J. W.; Bower, D. K.; Dalton, D. M.; Keister, J. B.; Churchill, M. R. Organometallics 1989, 8, 492-497. (d) Churchill, M. B.; Buttrey, L. A.; Keister, J. B.; Ziller, J. W.; Janik, T. S.; Striejewske, W. S. Organometallics 1990, 9, 766-773. (e) Adams, K. J.; Barker, J. J.; Knox, S. A. R.; Orpen, A. G. J. Chem. Soc., Dalton Trans. 1996, 975-988. (f) Blake, A. J.; Dyson, P. J.; Gaede, P. E.; Johnson, B. F. G.; Parsons, S. Organometallics 1996, 15, 4100-4103. (g) Bruce, M. I.; Humphrey, P. A.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 1997, 545-546, 207-218. (h) Hsu, M.-A.; Yeh, W.-Y.; Lee, G.-H.; Peng, S.-M. J. Organomet. Chem. 1999, 588, 32-41. (i) Xia, C.-G.; Bott, S. G.; Richmond, M. G. J. Chem. Crystallogr. 2003, 33, 681-687.

Figure 5. Molecular structure and labeling scheme of the cationic moiety of 11-BPh4 with thermal ellipsoids at the 40% probability level. The anionic moiety is omitted for clarity. One of the two independent molecules in the unit cell is shown. Table 3. Selected Bond Distances (Å) and Angles (deg) for 11 Ru(1)-Ru(2) Ru(1)-C(2) Ru(2)-Ru(3) Ru(2)-C(6) Ru(3)-C(6) C(3)-C(5) Ru(1)-Ru(3) Ru(1)-C(3) Ru(2)-C(1) Ru(2)-Ru(1)-Ru(3) Ru(2)-Ru(1)-C(4) Ru(3)-Ru(1)-C(4) C(2)-Ru(1)-C(4) Ru(1)-Ru(2)-C(2) Ru(3)-Ru(2)-C(2) C(1)-Ru(2)-C(6) Ru(1)-Ru(3)-C(1) Ru(2)-Ru(3)-C(1) C(1)-Ru(3)-C(4) Ru(1)-C(2)-Ru(2) C(2)-C(3)-C(4) Ru(1)-C(4)-Ru(3) Ru(2)-C(6)-Ru(3) Ru(2)-Ru(1)-C(1) Ru(3)-Ru(1)-C(1) C(1)-Ru(1)-C(2) Ru(1)-Ru(2)-Ru(3) Ru(1)-Ru(2)-C(6) Ru(3)-Ru(2)-C(6) C(2)-Ru(2)-C(6)

2.7116(3) 2.153(3) 2.7060(3) 2.023(3) 2.045(3) 1.516(4) 2.7247(3) 2.235(3) 1.993(3)

Ru(3)-C(1) C(2)-C(3) C(6)-O(1) Ru(1)-C(1) Ru(1)-C(4) Ru(2)-C(2) Ru(3)-C(4) C(3)-C(4)

59.705(9) 82.72(8) 47.06(8) 68.17(12) 51.67(9) 86.31(9) 95.69(12) 47.99(9) 47.23(9) 98.93(13) 81.08(11) 116.4(3) 81.24(11) 83.38(12) 47.03(9) 46.81(9) 93.62(12) 60.389(9) 94.44(9) 48.66(9) 80.74(13)

Ru(1)-Ru(3)-C(4) Ru(2)-Ru(3)-C(4) C(1)-Ru(3)-C(6) Ru(1)-C(2)-C(3) C(2)-C(3)-C(5) Ru(1)-C(4)-C(3) Ru(2)-C(6)-O(1) Ru(2)-Ru(1)-C(2) Ru(3)-Ru(1)-C(2) C(1)-Ru(1)-C(4) Ru(1)-Ru(2)-C(1) Ru(3)-Ru(2)-C(1) C(1)-Ru(2)-C(2) Ru(1)-Ru(3)-Ru(2) Ru(1)-Ru(3)-C(6) Ru(2)-Ru(3)-C(6) C(4)-Ru(3)-C(6) Ru(2)-C(2)-C(3) C(4)-C(3)-C(5) Ru(3)-C(4)-C(3) Ru(3)-C(6)-O(1)

1.994(3) 1.427(4) 1.175(4) 2.032(3) 2.164(3) 2.015(3) 2.018(3) 1.419(4) 51.70(9) 85.54(9) 94.95(13) 74.15(19) 121.8(3) 73.92(19) 139.0(3) 47.25(8) 83.26(9) 93.18(12) 48.26(9) 47.26(9) 99.20(13) 59.905(9) 93.53(9) 47.96(9) 79.98(13) 124.3(2) 121.6(3) 125.3(2) 137.5(3)

as those of 5a and 10, in spite of the difference in charge of the trimetallic core (C(2)-C(3), 1.427(4) Å; C(3)-Ru(4), 1.419(4) Å). In both 1H and 13C NMR spectra, signals stemming from the diruthenaallyl moiety of 11 appeared between those of neutral 5 and dicationic 10. The methine proton of the diruthenaallyl moiety of 11 was observed at δ 8.55 as a singlet, while those of 5a and 10 appeared at δ 8.24 and 10.09, respectively. The 13C signal of the R-carbon was observed at δ 182.4 as a doublet (JC-H ) 146.5 Hz), which also appeared between those of 5a (δ 174.6) and 10 (δ 195.4). The JC-H value was also an intermediate value. Thus, the chemical shift and the JC-H value of the diruthenaallyl moiety have a close relationship with the number of positive charges on the Ru3 core; as the positive charge increases, the methine signal shifts significantly downfield and


the JC-H value increases. This trend is also observed in the µ3η3-C3 complexes and reflects weakening of the shielding effect and reduced back-donation from the three Ru atoms to the C3 moiety in the dicationic species. Since complex 11 is monocationic, deprotonation should take place during the reaction. It is noteworthy that the monocationic µ3-η3-C3 complex 8 did not react with carbon monoxide, even under more forcing conditions. Thus, the reaction took place at the dicationic metal centers, and deprotonation is induced by the coordination of carbon monoxide.

Conclusion Lowering of the HOMO level by introduction of a µ3methylidyne ligand into the cluster core was confirmed by the cyclic voltammograms of 5a and 3a, and introduction of the µ3-methylidyne group enables us to isolate the paramagnetic 47e intermediate 6 as well as the dicationic mixture 7a,b. The cyclic voltammograms shown in Figure 1 indicate that the first oxidation did not involve skeletal rearrangement and that the second oxidation step involves skeletal rearrangement from the µ3-diruthenaallyl to the µ3-η3-C3 ring structure. The extremely large JC-H value of 196.6 Hz observed in 7a strongly indicates that complex 7a adopts a µ3-η3-C3 ring structure. The C3 ring structure was confirmed in the deprotonated complex 8 by means of X-ray diffraction studies. Thus, the oxidation of 5a, affording the monocationic µ3-η3-C3 complex 8, proceeded by way of an EEC mechanism: i.e., (i) two steps of 1e oxidation, (ii) C-C bond formation on the Ru3 cluster, and (iii) deprotonation. This is a quite rare example of C-C bond formation occurring at a highly oxidized Ru3 center, while C-C bond cleavage upon oxidation was reported for Cp2Ru2(µ-cyclo-C8H8)4a,b and (η5C5H4Me)4Fe4(µ-η2:η2-HCCH)(µ3-CO)2.4c,d In these complexes, the C-C bond was re-formed by reduction. The µ3-diruthenaallyl skeleton has been transformed to the µ3-η3-C3 ring structure, probably due to compensation of the electronic perturbation derived from the two-electron oxidation. The notable features of the µ3-η3-C3 ring of 8 are its unusually long C-C bond distances and large JC-H values. These are most likely due to the carbenic character of the bridging carbons. The DFT calculations showed that the C3 ligand was a resonance hybrid between the tris(µ-carbene) and µ3-cyclopropenyl structures. Although only 7a,b were spectroscopically detected in the dicationic mixture, contribution of the dicationic µ3-diruthenaallyl complex 9 in the equilibrated mixture would be implied by the reaction of the dicationic mixture 7a,b with CH2Cl2 and CO. The reaction of 7a,b with CH2Cl2 or CO afforded the dicationic µ-chloro µ3-diruthenaallyl complex 10 and the monocationic µ-carbonyl µ3-diruthenaallyl complex 11, respectively. Although the mechanism of C-C bond cleavage by the coordination of the lone pair of a chlorine atom or CO to the dicationic metal center is not negligible at present, isolation of the dicationic diruthenaallyl complex 10 suggests that skeletal rearrangement between the µ3-η3-C3 ring and µ3-dimetallaallyl structures on the dicationic triruthenium core would be equally facile. We are now continuing research on the reactivities of the dicationic triruthenium clusters, especially functionalization of the hydrocarbyl ligand on the dicationic cluster.

Experimental Section General Procedures. All manipulations were carried out under an atmosphere of argon. All compounds were handled using Schlenk techniques. Dehydrated toluene, tetrahydrofuran, and pentane were purchased from Kanto Chemicals and stored under an argon atmo-

Organometallics, Vol. 26, No. 6, 2007 1357 sphere. Diethyl ether was dried over sodium-benzophenone ketyl and stored under an argon atmosphere. Acetone-d6 was dried over MS-4A and stored under an argon atmosphere. Complex 5a was prepared according to a method previously reported in ref 10. IR spectra were recorded on a Nicolet AVATAR 360 ESP spectrophotometer. 1H and 13C NMR spectra were recorded on a Varian INOVA-400 Fourier transform spectrometer with tetramethylsilane as an internal standard. Elemental analyses were performed on a Perkin-Elmer 2400II instrument. ESI-MS spectra were recorded on a JEOL JMS-T100CS spectrometer. Cyclic voltammograms were performed using a HOKUTO DENKO HSV-100 voltammetric analyzer interfaced to a personal computer. The working electrode was platinum, and the counter electrode was a platinum wire. The reference electrode was a silver wire housed in a glass tube sealed with a porous Vycor tip and filled with a 0.1 M solution of AgNO3 in acetonitrile. The data obtained relative to a reference electrode (Ag/Ag+) were converted to the potential relative to the redox potential of ferrocene, which was measured under the same conditions at the same time. Tetrabutylammonium hexafluorophosphate (TBAPF6; Wako) was recrystallized from THF, dried under vacuum, and stored under an argon atmosphere. A concentration of ∼1 mM of complexes 5a and 3a in 0.1 M TBAPF6 in THF was used. X-ray Structure Determination. X-ray-quality crystals of 8-BPh4, 10-PF6, and 11-BPh4 were obtained directly from the preparations described below and mounted on glass fibers. Diffraction experiments of 8-BPh4, 10-PF6, and 11-BPh4 were performed on a Rigaku RAXIS-RAPID imaging plate diffractometer with graphite-monochromated Mo KR radiation (λ ) 0.710 69 Å) at -120, -100, and -150 °C, respectively. The structures were solved by the Patterson method and subsequent Fourier difference techniques. All non-hydrogen atoms were refined anisotropically by full-matrix least-squares calculations on F2 using the SHELX97 program package. Neutral atom scattering factors were obtained from the standard sources.21 Crystal data and results of the analyses are given in Table 4. Preparation of [(Cp*Ru)3(µ3-CH)(µ3-η1:η3:η1-CHCMeCH)(µ-H)]+ (6). Toluene (10 mL) and (Cp*Ru)3(µ3-CH)(µ3-CHCMeCH)(µ-H) (5a; 86.1 mg, 0.11 mmol) were charged in a 50 mL reaction flask. After [Cp2Fe](PF6) (36.7 mg, 0.11 mmol) was added to the solution at room temperature, the solution was vigorously stirred for 2 h. The solution immediately turned from red to purple, and a purple precipitate was formed. The precipitate was separated by removing the supernatant including ferrocene and rinsed three times with 2 mL of toluene. The residual solid was then dried under reduced pressure, and 81.7 mg of a hexafluorophosphate salt of 6 was obtained as a purple solid (0.089 mmol, 80%). Methanol (10 mL) and the hexafluorophosphate salt of 6 (81.7 mg, 0.089 mmol) were charged in a 50 mL reaction flask. After an excess amount of NaBPh4 (158.4 mg, 0.463 mmol) was added to the solution, the reaction flask was vigorously stirred at room temperature for 2 h. The precipitate was separated by decantation to remove the supernatant including NaPF6 and remaining NaBPh4. The residual solid was then dried under reduced pressure, and a 51.7 mg amount of a tetraphenylborate salt of 6 was obtained as a purple solid (53%). 6-PF6: 1H NMR (400 MHz, 25 °C, acetone-d6) δ 43.67 (brs, w1/2 ) 2100 Hz). 6-BPh4: 1H NMR (400 MHz, 25 °C, acetone-d6): δ 6.78 (t, JHH ) 7.2 Hz, 4H, p-BPh4), 6.90 (dd, JHH ) 7.2, 7.2 Hz, 8H, m-BPh4), 7.31, (m, 8H, o-BPh4), 43.68 (br s, w1/2 ) 2120 Hz, 45H, C5Me5). Anal. Calcd for C59H72BRu3: C, 64.70; H, 6.63. Found: C, 64.24; H, 6.35. Due to its instability toward air, the complex 6-BPh4 partially decomposed during carbon analysis. ESI mass spectra for 6-PF6 and 6-BPh4 could not be obtained, due to the fragmentation into bi- and monometallic compounds during ionization. (21) International Tables for X-ray Crystallography; Kynoch Press: Birmingham, U.K., 1975; Vol. 4.


Takao et al.

Table 4. Crystallographic Data for 8-BPh4, 10-PF6, and 11-BPh4 8-BPh4 empirical formula formula wt cryst descripn cryst color cryst size (mm) crystallizing soln cryst syst space group lattice params a (Å) b (Å) c (Å) β (deg) V (Å3) Z Dcalcd (g cm-3) measmt temp (°C) µ(Mo KR) (mm-1) diffractometer radiation monochromator 2θmax (deg) no. of rflns collected no. of indep rflns no. of obsd rflns (>2σ) abs cor type abs transmissn min max R1 (I > 2σ(I)) wR2 (I > 2σ(I)) R1 (all data) wR2 (all data) no. of data/restraints/params GOF largest diff peak, hole (e Å-3)

10-PF6

11-BPh4

(a) Crystal Data C59H71BRu3 1094.18 platelet red 0.50 × 0.20 × 0.20 THF (-30 °C) monoclinic P21/n (No. 14)

C36H53Cl3F12P2Ru3 1185.28 platelet green 0.60 × 0.20 × 0.20 CH2Cl2 (-30 °C) monoclinic P21/n (No. 14)

C60H71BORu3 1122.19 platelet red 0.40 × 0.10 × 0.05 MeOH (-30 °C) monoclinic P21/n (No. 14)

19.918(4) 13.650(2) 20.532(4) 115.466(8) 5040.2(17) 4 1.442 -120 0.925

11.9434(2) 16.1553(3) 22.2949(3) 96.7400(6) 4272.05(12) 4 1.843 -100 1.389

16.56750(10) 17.3124(2) 35.4645(3) 95.5860(4) 10123.74(16) 8 1.473 -150 0.924

(b) Intensity Measurements RAXIS-RAPID RAXIS-RAPID Mo KR Mo KR graphite graphite 60 60 47 921 50 503 11 987 (Rint ) 0.0327) 12 349 (Rint ) 0.0199) 10 307 11 173 empirical empirical

RAXIS-RAPID Mo KR graphite 60 89 389 29 676 (Rint ) 0.0328) 21 522 empirical

0.6610 1.0000

0.9085 1.0739

0.4894 0.7685

(c) Refinement (Shelxl-97) 0.0280 0.0347 0.0702 0.0851 0.0320 0.0393 0.0721 0.0877 11 502/0/597 12 349/0/534 1.029 1.040 0.865, -1.498 2.413, -1.459

Reaction of 3a with an Equimolar Amount of [Cp2Fe][PF6]. Toluene (10 mL) and (Cp*Ru)3(µ-H)4(µ3-η1:η3:η1-CHCHCMe) (81.9 mg, 0.107 mmol) were charged in a reaction flask. After [Cp2Fe][PF6] (35.7 mg, 0.108 mmol) was added to the solution at 0 °C, the solution was vigorously stirred for 1 h. The solution turned from dark green to brown. Removal of the solvent under reduced pressure afforded 0.122 g of brown precipitate. The 1H NMR spectrum of the mixture showed that all of 3a was consumed and 4a was formed in 33% yield as the main product. In addition to 4a, formation of ferrocene and some other unidentified species was observed. Among the unidentified signals, a broad signal derived from a paramagnetic compound, which was considered to be a oneelectron-oxidized product of 3a, was observed at δ 4.51 (w1/2 ) 43.4 Hz), although this compound was not isolated and completely characterized. The yield of 4a was estimated on the basis of the intensity of the Cp* signals of 4a, using the produced ferrocene as an internal standard. Reduction of Complex 6. THF (10 mL) and the hexafluorophosphate salt of 6 (47.2 mg, 0.0443 mmol) were charged in a reaction flask. After 1 equiv of (C5Me5)2Co (15.3 mg, 0.0464 mmol) was added to the solution at room temperature, the solution was vigorously stirred for 2 h. The solution turned from purple to red. After the solvent was removed under reduced pressure, the residual solid was dissolved in 3 mL of toluene. The product was then purified by the use of column chromatography on neutral alumina (Merck Art. No. 1097) with toluene. A red band was collected, and a 28.2 mg amount of 5a was obtained as a red solid by removal of the solvent in vacuo (0.0363 mmol, 82%). Formation of 5a was confirmed by comparing its 1H NMR spectrum with that of an authentic sample prepared by the method described in ref 10.

0.0452 0.0884 0.0715 0.0975 28 750/0/1229 1.052 2.102, -2.548

Preparation of [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H2Me)(µ-H)]2+ (7a,b). Toluene (10 mL) and (Cp*Ru)3(µ3-CH)(µ3-CHCMeCH)(µ-H) (5a; 92.7 mg, 0.12 mmol) were charged in a 50 mL reaction flask. After [Cp2Fe](PF6) (74.0 mg, 0.24 mmol) was added to the solution at room temperature, the solution was vigorously stirred for 2 h. The solution turned from red to brown, and a brown precipitate was formed. The precipitate was then separated by removal of the supernatant including ferrocene. The brown solid was rinsed three times with 5 mL of toluene. The residual solid was dried under reduced pressure, and 0.116 g of the mixture of hexafluorophosphate salts of 7a,b was obtained as a brown solid (0.11 mmol, 92%). Since 7a and 7b equilibrated with each other in solution, they were not separated from each other. The ratio between 7a,b at -70 °C was estimated as 67:33 on the basis of the 1H NMR spectrum of the mixture measured at this temperature. 7a: 1H NMR (400 MHz, -70 °C, acetone-d6) δ -15.37 (s, 1H, Ru-H), 2.06 (obscured by the residual proton signal of acetone-d6, C5Me5), 2.08 (s, 15H, C5Me5), 2.271 (s, 3H, µ3-η3-C3H2Me), 9.18 (s, 2H, µ3-η3-C3H2Me), 16.69 (s, 1H, µ3-CH); 13C NMR (100 MHz, -70 °C, acetone-d6) δ 10.5 (q, JCH ) 128.3 Hz, C5Me5), 10.8 (q, JCH ) 127.5 Hz, C5Me5), 30.7 (obscured by the signal of acetone-d6, µ3-η3-C3H2Me), 104.7 (s, C5Me5), 105.1 (s, C5Me5), 132.1 (s, µ3-η3-CHCMeCH-), 171.8 (d, JCH ) 196.9 Hz, µ3-η3-CHCMeCH-), 356.3 (d, JCH ) 166.8 Hz, µ3-CH). 7b: 1H NMR (400 MHz, -70 °C, acetone-d6) δ -15.00 (br s, 1H, Ru-H), 2.265 (s, 3H, µ3-η3-C3H2Me), 6.89 (dd, JHH ) 2.4, 2.4 Hz, 1H, µ3-η3-C3HHMe), 9.27 (d, JHH ) 2.4 Hz, 1H, µ3-η3-C3HHMe), 16.78 (s, 1H, µ3-CH) (the 1H signals of the C5Me5 groups of 7b were obscured by the residual proton signals of acetone-d6 and the C5Me5 signals of 7a); 13C NMR (100 MHz, -70 °C, acetone-d6) δ 10.4 (C5Me5), 10.7 (C5Me5), 104.5 (s, C5-

Rearrangement of a Dimetallaallyl Ligand Me5), 105.1 (s, C5Me5), 105.2 (s, C5Me5) (other 13C signals of 7b were not observed, due to low distribution of 7b in the solution); IR (ATR, cm-1) 834, 1023, 1075, 1108, 1376, 1424, 1451, 1480, 2925, 2965. Anal. Calcd for C35H52F12P2Ru3: C, 39.44; H, 4.92. Found: C, 40.03; H, 4.95. Since the solvent could not be removed from the dicationic mixture completely, the data of carbon analysis for the mixture did not fit well with the calculated value. An attempt to obtain ESI mass spectra for the dicationic mixture 7a,b resulted in deprotonation during ionization, and the same spectrum as for 8 was obtained. Preparation of (Cp*Ru)3(µ3-CH)(µ3-η1:η3:η1-CHCHCH)(µH) (5b). Heptane (10 mL) and the µ3-η1:η3:η1-allyl complex (Cp*Ru)3(µ3-η1:η3:η1-CHCHCMe)(µ-H)47 (56.2 mg, 0.073 mmol) were charged in a glass autoclave. The reaction solution was then heated to 180 °C for 6 days. After the solvent was evaporated under reduced pressure, the residual solid was dissolved in 3 mL of toluene. The product was purified by the use of column chromatography on neutral alumina (Merck Art. No. 1097) with toluene. The first reddish brown band was collected, and removal of the solvent under reduced pressure afforded 32.0 mg of 5b as a red solid (0.042 mmol; 57%). 1H NMR (400 MHz, 25 °C, benzened6): δ -22.07 (d, JHH ) 3.2 Hz, 1H, Ru-H), 1.55 (s, 15H, C5Me5), 1.90 (s, 30H, C5Me5), 5.73 (dd, JHH ) 3.2, 5.6 Hz, 1H, µ3-η1:η3: η1-CHCHCH), 8.50 (d, JHH ) 5.6 Hz, 2H, µ3-η1:η3:η1-CHCHCH), 16.12 (s, 1H, µ3-CH). 13C NMR (100 MHz, 25 °C, benzene-d6): δ 11.2 (q, JCH ) 126.1 Hz, C5Me5), 11.8 (q, JCH ) 125.1 Hz, C5Me5), 91.4 (s, C5Me5), 93.2 (s, C5Me5), 101.8 (d, JCH ) 158.0 Hz, µ3-η1:η3:η1-CHCHCH), 175.6 (d, JCH ) 133.7 Hz, µ3-η1:η3:η1CHCHCH), 324.7 (d, JCH ) 158.0 Hz, µ3-CH). IR (ATR, cm-1): 877, 1025, 1372, 1453, 1473, 11556, 2894, 2964. Anal. Calcd for C34H50Ru3: C, 53.59; H, 6.61. Found C, 53.53; H, 6.83. Preparation of [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H3)(µ-H)]+ (7c). Toluene (10 mL) and (Cp*Ru)3(µ3-CH)(µ3-η1:η3:η1-CHCHCH)(µH) (5b; 34.4 mg, 0.0450 mmol) were charged in a 50 mL reaction flask. After [Cp2Fe](PF6) (29.2 mg, 0.0882 mmol) was added to the solution at room temperature, the solution was vigorously stirred for 2 h. The solution turned from red to brown and formed a brown precipitate. The precipitate was separated by removal of the supernatant including ferrocene. The brown solid was rinsed three times with 5 mL of toluene. The residual solid was dried under reduced pressure, and 32.3 mg of the hexafluorophosphate salt of 7c was obtained as a brown solid (0.042 mmol, 94%). 1H NMR (400 MHz, -70 °C, acetone-d6): δ -15.05 (br s, 1H, Ru-H), 2.08 (s, 30H, C5Me5), 2.11 (s, 15H, C5Me5), 7.04 (brd, 1H, JHH ) 3.2 Hz, µ3-η3-CHCHCH-), 9.24 (br d, JHH ) 2.4 Hz, 2H, µ3-η3CHCHCH-), 16.65 (s, 1H, µ3-CH). 13C NMR (100 MHz, -70 °C, acetone-d6): δ 10.7 (q, JCH ) 128.3 Hz, C5Me5), 10.8 (q, JCH ) 128.2 Hz, C5Me5), 104.9 (s, C5Me5), 105.4 (s, C5Me5), 116.4 (d, JCH ) 209.1 Hz, µ3-η3-CHCHCH-), 166.1 (d, JCH ) 198.8 Hz, µ3-η3-CHCHCH-), 355.8 (d, JCH ) 174.5 Hz, µ3-CH). IR (ATR, cm-1): 837, 1023, 1378, 1425, 1451, 1474, 2913, 2964. Since the solvent could not be removed from the dicationic complex completely, the data of carbon analysis for 7c did not fit well with the calculated value. An attempt to obtain ESI mass spectra for the dicationic complex 7c also resulted in deprotonation during ionization, as found in the dicationic mixture 7a,b. Preparation of [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H2Me)]+ (8). Acetone (10 mL) and the dicationic mixture of hexafluorophosphate salts of [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H2Me)(µ-H)]2+ (7a,b; 135.4 mg, 0.13 mmol) were charged in a 50 mL reaction flask. After 3 equiv of triethylamine (40 µL) was added to the solution at room temperature, the solution was vigorously stirred for 2 h. The solution turned from brown to brownish yellow. After the solvent was removed under reduced pressure, the residual brownish yellow solid was then dissolved in 2 mL of THF. The product was purified by the use of column chromatography on alumina (Merck Art. No. 1097) with THF. The yellow band was collected, and removal of

Organometallics, Vol. 26, No. 6, 2007 1359 the solvent in vacuo afforded 103.3 mg of the hexafluorophosphate salt of 8 as a yellow crystalline solid (0.11 mmol; 70%). A single crystal suitable for diffraction studies was prepared from a cold THF solution of a tetraphenylborate salt of 8, which was obtained by the anion exchange of PF6- with BPh4- using an excess amount of NaBPh4. 1H NMR (400 MHz, 23 °C, acetone-d6): δ 1.84 (s, 30H, C5Me5), 1.86 (s, 15H, C5Me5), 2.58 (s, 3H, µ3-η3-C3H2Me), 7.77 (s, 2H, µ3-η3-C3H2Me), 17.08 (s, 1H, µ3-CH). 13C NMR (100 MHz, 23 °C, acetone-d6): δ 10.9 (q, JCH ) 127.4 Hz, C5Me5), 11.2 (q, JCH ) 127.5 Hz, C5Me5), 30.5 (obscured by the residual proton signal of acetone-d6; µ3-η3-C3H2Me), 98.5 (s, C5Me5), 109.9 (s, C5Me5), 158.2 (d, JCH ) 189.1 Hz, µ3-η3-CHCMeCH-), 162.6 (s, µ3-η3-CHCMeCH-), 354.5 (d, JCH ) 165.6 Hz, µ3-CH). IR (ATR, cm-1): 835, 876, 1023, 1071, 1105, 1262, 1376, 1425, 1451, 1474, 2910, 2964. Anal. Calcd for C35H51F6PRu3: C, 45.70; H, 5.59. Found: C, 45.09; H, 5.59. Although the data of the carbon analysis did not fit with the calculated value in spite of several attempts, the composition of the cationic moiety of 8 was confirmed by the ESI-MS spectrum. ESI-MS(+) (m/z (relative intensity)): 777 (100) (calcd for C35H51Ru3+, 777). Protonation of the Monocationic Complex 8. The hexafluorophosphate salt of 8 (15.2 mg, 0.014 mmol) and dichloromethaned2 (0.4 mL) were charged in an NMR tube. After an excess amount of trifluoromethanesulfonic acid was added to the solution at room temperature, the solution was vigorously stirred for 10 min. Formation of the dicationic mixture 7a,b was confirmed by the 1H NMR spectra. 1H NMR (400 MHz, 23 °C, dichloromethane-d2): δ -15.48 (br, Ru-H), 7.91 (br, µ3-C3H2Me), 15.81 (br, µ3-CH). Reduction of the Dicationic Mixture 7a,b. The mixture of hexafluorophosphate salts of the dicationic complexes 7a,b (30.3 mg, 0.028 mmol) and THF (10 mL) were charged in a reaction flask. A 0.5 M DME solution of sodium naphthalenide (0.15 mL, 0.26 mmol) was then added to the solution at 25 °C. While complexes 7a,b were suspended in the solvent at the beginning, they gradually dissolved. The solution was allowed to react for 2 h with vigorous stirring, and it turned red. After the solvent was removed under reduced pressure, the product was dissolved in 3 mL of toluene and purified by the use of column chromatography on alumina (Merck Art. No. 1097) with toluene. Removal of the solvent in vacuo afforded 20.7 mg of the mixture 5a,c as a red solid (94% yield). The ratio between 5a and 5c was estimated as 65:35 by the 1H NMR spectrum. Formation of 5a was confirmed by comparing its 1H NMR spectrum with that of an authentic sample prepared by the method described in ref 10. 5c: 1H NMR (400 MHz, 25 °C, benzene-d6) δ -22.77 (d, JHH ) 4.0 Hz, 1H, Ru-H), 1.52 (s, 15H, C5Me5), 1.83 (s, 15H, C5Me5), 1.88 (s, 15H, C5Me5), 2.44 (s, 3H, µ3-CMeCHCH), 5.43 (dd, JHH ) 5.6, 4.0 Hz, 1H, µ3CMeCHCH), 8.48 (d, JHH ) 5.6 Hz, 1H, µ3-CMeCHCH), 16.40 (s, 1H, µ3-CH); 13C NMR (100 MHz, 25 °C, benzene-d6) δ 10.9 (q, JCH ) 125.9 Hz, C5Me5), 11.4 (q, JCH ) 125.6 Hz, C5Me5), 11.7 (q, JCH ) 125.0 Hz, C5Me5), 35.6 (q, JCH ) 122.2 Hz, µ3CMeCHCH), 91.1 (s, C5Me5), 93.5 (s, C5Me5), 93.6 (s, C5Me5), 104.4 (d, JCH ) 155.0 Hz, µ3-CMeCHCH), 177.2 (d, JCH ) 140.3 Hz, µ3-CMeCHCH), 183.2 (s, µ3-CMeCHCH), 326.5 (d, JCH ) 157.1 Hz, µ3-CH). Preparation of [(Cp*Ru)3(µ3-CH)(µ3-η1:η3:η1-CHCMeCH)(µ-Cl)]2+ (10). Hexafluorophosphate salts of the dicationic complexes [(Cp*Ru)3(µ3-CH)(µ3-η3-C3H2Me)(µ-H)]2+ (7a,b; 78.1 mg, 0.073 mmol) and dichloromethane (5 mL) were charged in a sealed tube. The solution was vigorously stirred for 12 h at 100 °C. The solution turned from brown to green. Removal of the solvent under reduced pressure afforded a mixture of hexafluorophosphate salts of [(Cp*Ru)3(µ3-CH)(µ3-CHCMeCH)(µ-Cl)]2+ (10) and the monocationic complex 8 in a ratio of 74:26 (determined by 1H NMR). The residual solid was rinsed three times with 2 mL of THF to remove 8. The residual solid was dried under reduced pressure, and 7.7 mg of the hexafluorophosphate salt of 10 was obtained as

1360 Organometallics, Vol. 26, No. 6, 2007 a green solid (10% yield). A single crystal of 10-PF6 suitable for the X-ray diffraction studies was obtained from the dichloromethane solution of the mixture of 10 and 8 at -30 °C. X-ray crystallography showed that one dichloromethane molecule was contained in the unit cell. Elemental analysis was measured for this single crystal, which contained a crystallizing solvent. 1H NMR (400 MHz, 23 °C, acetone-d6): δ 1.97 (s, 15H, C5Me5), 2.04 (s, 30H, C5Me5), 2.47 (s, 3H, µ3-CHCMeCH), 10.09 (s, 2H, µ3-CHCMeCH), 15.01 (s, 1H, µ3-CH). 13C NMR (100 MHz, 23 °C, acetone-d6): δ 11.0 (q, JCH ) 128.6 Hz, C5Me5), 11.2 (q, JCH ) 128.6 Hz, C5Me5), 21.3 (q, JCH ) 128.6 Hz, µ3-CHCMeCH), 105.9 (s, C5Me5), 110.0 (s, C5Me5), 112.6 (s, µ3-CHCMeCH), 195.4 (d, JCH ) 166.7 Hz, µ3-CHCMeCH), 330.8 (d, JCH ) 173.8 Hz, µ3-CH). IR (ATR, cm-1): 832, 875, 1020, 1079, 1114, 1381, 1432, 1460, 1493, 2913, 2971, 3001. Anal. Calcd for C36H53Cl3F12P2Ru3-: C, 36.48; H, 4.51. Found: C, 36.67; H, 4.49. Preparation of [(Cp*Ru)3(µ3-CH)(µ3-η1:η3:η1-CHCMeCH)(µ-CO)]+ (11). Dichloromethane (5 mL) and hexafluorophosphate salts of the dicationic complexes [(Cp*Ru)3(µ3-CH)(µ3-CHCMeCH)(µ-H)]2+ (7a,b; 78.1 mg, 0.073 mmol) were charged in a 50 mL reaction flask. The reaction flask was then degassed, and 1 atm of CO was subsequently introduced at -78 °C. The reaction flask was gradually warmed to 25 °C and vigorously stirred for 24 h. The solution turned from brown to yellow. The reaction solution was evaporated under reduced pressure. The residual solid was dissolved in THF, and the product was purified by the use of column chromatography on alumina (Merck Art.) with THF and MeOH. The hexafluorophosphate salt of 11 was obtained as a dark yellow solid on removal of the solvent under reduced pressure (65.1 mg, 96%). The tetraphenylborate salt of 11 was obtained by the treatment of the hexafluorophosphate salt of 11 (65.1 mg, 0.071 mmol) with an excess amount of NaBPh4 (75.1 mg, 0.22 mmol) in 10 mL of methanol. A dark yellow solid was immediately formed, and the precipitate was rinsed three times with 2 mL of methanol. The precipitate was then dried under reduced pressure, and 73.3 mg of tetraphenylborate salt of 11 was obtained as a yellow solid (92%). 11-PF6: 1H NMR (400 MHz, 23 °C, acetone-d6) δ 1.83 (s,

Takao et al. 15H, C5Me5), 1.89 (s, 30H, C5Me5), 2.34 (s, 3H, µ3-CHCMeCH), 8.55 (s, 2H, µ3-CHCMeCH), 15.50 (s, 1H, µ3-CH); 13C NMR (100 MHz, 23 °C, acetone-d6) δ 10.3 (q, JCH ) 126.9 Hz, C5Me5), 11.1 (q, JCH ) 126.9 Hz, C5Me5), 21.6 (q, JCH ) 124.6 Hz, µ3CHCMeCH), 99.1 (s, C5Me5), 103.0 (s, C5Me5), 106.6 (s, µ3-CHCMeCH), 182.4 (d, JCH ) 146.5 Hz, µ3-CHCMeCH), 239.6 (s, µ-CO), 326.1 (d, JCH ) 165.6 Hz, µ3-CH); IR (ATR, cm-1): 836, 1024, 1375, 1456, 1786 (νCO), 2905. 11-BPh4: 1H NMR (400 MHz, 23 °C, acetone-d6) δ 1.83 (s, 15H, C5Me5), 1.89 (s, 30H, C5Me5), 2.33 (s, 3H, µ3-CHCMeCH), 6.76 (t, JHH ) 7.2 Hz, 4H, p-BPh4), 6.91 (dd, JHH ) 7.2, 7.2 Hz, 8H, m-BPh4), 7.33, (m, 8H, o-BPh4), 8.56 (s, 2H, µ3-CHCMeCH), 15.49 (s, 1H, µ3-CH). Anal. Calcd for C60H71BORu3: C, 64.22; H, 6.38. Found: C, 63.63; H, 6.49. Although the data of carbon analysis for 11-BPh4 did not fit well with the calculated value in spite of several attempts, the composition of the cationic moiety of 11-BPh4 was confirmed by an ESI-MS spectrum. ESI-MS(+) (m/z (relative intensity)): 804 (100) (calcd for C36H51ORu3+, 804).

Acknowledgment. This work is supported by the grants No. 18105002 (Scientific Research (S)) from Japan Society of the Promotion of Science and No. 18064007 (Priority Area “Synergy of Elements”) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. This work was partly supported by the 21st Century COE program of the Japan Society for the Promotion of Science. We acknowledge Kanto Chemical Co., Inc., for generous gifts of pentamethylcyclopentadiene. Supporting Information Available: Results of the X-ray diffraction studies and CIF files giving crystallographic data for 8-BPh4, 10-PF6, and 11-BPh4 and text and a figure giving the results of a kinetic study on the deprotonation of the dicationic mixture 7a,b in acetone/methanol. This material is available free of charge via the Internet at http://pubs.acs.org. OM060932X

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